Production of acetylene and olefins by pyrolysis of hydrocarbons



April 26, 1966 e. FAUSER 3,248,445

PRODUCTION OF ACETYLENE AND OLEFINS BY PYROLYSIS OF HYDROCARBONS Filed Dec. 28, 1960 OXYGEN and WATER 5 COMBUSTION WATER T T CHAMBER FUEL GAS 6 SATURATE WATER T 7 GASOL- 5% /HEAT EXCHANGER OXYGEN COMPRESSOR United States Patent 3,248,445 lPRQDUCTION 0F ACETYLENE AND OLEFINS BY PYROLYSKS 0F HYDROCARBONS Giacomo Fauser, Novara, Italy, assignor to Montecatini, Societa Generals per lIndustria Mineraria e Chimica,

a corporation of Italy FiledDec. 28, 1960, Ser. No. 78,919 Claims priority, application Italy, Dec. 31, 1959, 21,733/59 6 Claims. (Cl. 260-679) This invention relates to an improvement in processes for making acetylene and olefins by pyrolysis of hydrocarbons.

Many methods are known for producing acetylene and olefins by pyrolysis of hydrocarbons in a stream of gas that is at a high temperature. Said methods are operated under a pressure very close to atmospheric, because it was thought that the equilibrium of the reaction promoting the formation of acetylene was hindered by increasing the ressure.

I have now found that this is not correct. When the pyrolysis of hydrocarbons is carried out under suitable conditions, yields of acetylene and olefins are obtained substantially equal to those obtainable under atmospheric pressure, even if the pressure is raised up to 10 atm., and above, viz. to atm.

Since the gases produced by the reaction must be compressed to separate acetylene and ethylene, the pyrolysis of hydrocarbons under pressure results in very great economy, both in plant costs and in power consumption, as compared with pyrolysis processes operating at atmospheric pressure.

The invention has another significant advantage. The gases leaving the furnace are cooled with water. This results in the recovery of a large amount of heat at a temperature higher than 150 C. This heat can be used to provide the heat required by the plant. A marked saving in the cost ofsteam is thus achieved.v Steam is needed in the combustion zone to avoid excessive temperatures.

I have found that, in order to obtain satisfactory acetylene and ethylene yields by pyrolysis of a light paraffin base gasoline at a pressure of 10 atm. (absolute atmospheres), is is necessary that its flow rate be higher than 800 kg./hr./dm. of reaction chamber capacity.

When the pyrolysis pressure is increased or lowered, it is necessary to increase or lower the hourly flow rate of the gasoline accordingly. This is an outstanding advantage of the new process. When the pressure is increased it is feasible to employ pyrolysis furnaces having a productive capacity of several tens of tons per day of acetylene and olefins.

Before introduction into the furnace, the gasoline should be preheated to the highest temperature permitted by its heat stability. For this purpose, it is advisable to mix the evaporated gasoline with steam before introducing it into the superheater.

The pyrolysis is carried out in a stream of hot gases. The said high temperature gas stream required to effect the pyrolysis of the gasoline is produced by combustion, in the presence of oxygen, of a portion of the residual gas produced in the same plant, after separation of acetylene and ethylene. In order to attain high thermal efficiency, it is necessary to provide for complete combustion of the hydrocarbon, by using gas to oxygen ratios very close to the stoichiometric values. However, in order to avoid excessive temperatures, it is necessary to add a considerable amount of steam in the combustion chamber. The steam is easily separated from the gases leaving the furnace by condensation, so that it does not hinder the operations required for separation of the acetylene and ethylene. However, the supplying of steam affects the cost of the products appreciably.

, 3,248,445 Patented Apr. 26, 1966 "ice The present invention provides an economical method for supplying the required steam, by utilizing the heat available in the reaction products.

The accompanying drawing diagrammatically illustrates the operation of the plant.

The furnace comprises a cylindrical vertical stainiess steel chamber 6 which is cooled by evaporation of water contained in an external coaxial jacket. It is advantageous to keep the vapor pressure in the jacket comparatively high, to avoid excessive heat losses in the combustion chamber, and in any case the vapor pressure should be higher than the pressure at which the hydrocarbon is injected into the furnace. A pressure above ten atmospheres is advantageous.

The oxygen and the fuel gas coming from compressors 1 and 2 are introduced into the saturator columns 3. and 4 the functions of which are described below. After preheating in 5, the oxygen and fuel gas are introduced into the combustion chamber 6.

The fuel gas introduced into column 4 may be replaced in part by a corresponding amount of gasoline coming from pump 19. The gasoline to be pyrolyzed is injected into the furnace through the nozzles 7 and 9.

Due to the elevated temperature, the formation of acetylene prevails in the reaction zone 3. In the zone 10, where the temperature goes down to 800 C., the formation of olefins prevails.

Finally, the reaction products are quenched with water sprayed by nozzles 11. The hot water collected at the bottom is conveyed into the column 4 by pump 15, to saturate the fuel gas with moisture. The vapor-gas ratio is adjusted by varying the water flow rate.

The gases leaving the furnace first pass through the heat exchanger 13. The water needed to moisten the oxygen in column 3 is preheated in the upper part of exchanger 13, being recirculated by pump 18. The gases are then cooled in refrigerator 16 in which the heavier fractions of the hydrocarbons produced are condensed together with the steam. The heavier hydrocarbons separate in the decanter 17 and are utilized as fuels. The gases leaving vessel 14 are treated to obtain acetylene and ethylene.

The process has considerable flexibility, and permits variation of the acetylene to ethylene ratio over a wide range, in accordance with the programs of industrial utilization.

Reference is made to my copending application Serial No. 757,740, filed August 28, 1958, which corresponds to Belgian Patent No. 571,587.

I claim:

1. A process for production of acetylene and ethylene, comprising pyrolyzing a hydrocarbon in a stream of hot combustion gases and steam, the steam being supplied to the combustible gas and to the oxygen employed to furnish the combustion gases by saturation with hot water heated by utilizing the heat of the reaction products, the process being carried out at about ten to twenty atmospheres absolute pressure, the hydrocarbon to be pyrolyzed being gasoline vapor, the gasoline vapor being preheated prior to introduction into the pyrolysis zone, steam being introduced into the gasoline vapor before said preheating.

2. A process for producing acetylene and ethylene by pyrolysis of a light paraffin base gasoline, comprising separately passing a hydrocarbon to be pyrolyzed, oxygen, and a gasoline fuel gas into a pyrolysis zone which is at a pressure of at least ten atmospheres the flow rate of the gasoline vapor being at least 800 kilograms per hour per cubic decimeter of pyrolysis chamber capacity, quenching the hot reaction gases with water, collecting the so heated water, passing the quenched gases through a heat exchange step in which another body of water is heated, said fuel gas and said oxygen being separately saturated with water by passing them in contact with the heated water, so as'to furnish steam to the pyrolysis zone.

3. A process for producing acetylene and ethylene by pyrolysis of a gasoline, comprising separately passing streams of the gasoline to be pyrolyzed, oxygen, and a hydrocarbon fuel gas, into a pyrolysis and combustion zone which is at a pressure above 3 atmospheres, quenching the hot reaction gases with Water, and supplying steam to the pyrolysis zone by passing the oxygen stream in contact with the hot water so produced, before introduction into the pyrolysis.

4. A process for producing acetylene and olefins, comprising separately compressing oxygen and fuel gas to a pressure of from 3 to about 20 atmospheres absolute, separately contacting the oxygen and fuel gas with hot water to produce respectively an oxygen-Water vapor mixture and a fuel gas-Water vapor mixture, separately preheating the mixtures in a first heat-exchange zone, passing the preheated mixtures into a combustion zone, the fuel gas-oxygen ratio being substantially the stoichiometric value corresponding to complete combustion, the steam serving to avoid excessive temperatures, introducing gasoline to be pyrolyzed into the combustion gases leaving the combustion zone, acetylene and olefines thereby forming, then quenching the hot gaseous reaction products with water, the quenching being at from 3 to about 20 atmospheres absolute, separating the reaction gas from the resulting hot water, which water is at a temperature above 150 C.

heating the mixtures in a first heat-exchange zone, passing the preheated mixtures into a combustion zone, the fuel gas-oxygen ratio being substantially the stoichiometric value corresponding to complete combustion, the steam serving to avoid excessive temperatures, introducing gasoline to be pyrolyzed into the combustion gases leaving the combustion zone, acetylene and olefines thereby forming, then quenching the hot gaseous reaction products with water, the quenching being at from 3 to about 20 atmospheres absolute, separating the reaction gas from the resulting hot water, which Water is at a temperature above 150 C., contacting the fuel gas with said hot water as aforesaid, passing the reaction gas to a second heat exchange zone in indirect heat exchange with water that was employed for said contacting with the oxygen, to heat the water, returning the latter water to again contact oxygen gas as aforesaid, and passing the reaction gas to a cooling zone to condense some of the hydrocarbons, leaving a mixture of acetylene and gaseous olefines.

6. A process for producing acetylene and olefines, comprising separately compressing oxygen and fuel gas to a pressure of from 3 to about 20 atmospheres absolute, separately contacting the oxygen and fuel gas with hot Water to produce respectively an oxygen-water vapor mixture and a fuel gas-Water vapor mixture, separately preheating the mixtures in a first heat-exchange zone, passing the preheated mixtures into a combustion zone, the fuel gas-oxygen ratio being substantially the stoichiometric value corresponding to complete combustion, the steam serving to avoid excessive temperatures, preheating gasoline to the highest temperature at which it remains stable, introducing the preheated gasoline mixed with steam into the combustion gases leaving the combustion zone, acetylene and olefines thereby forming, then quenching the hot gaseous reaction products with Water, the quenching being at from 3 to about 20 atmospheres absolute, separating the reaction gas from the resulting hot water, which Water is at a temperature above C., contacting the fuel gas with said hot water as aforesaid, passing the reaction gas to a second heat exchange zone in indirect heat exchange with water that was employed for said contacting with the oxygen, to heat the water, returning the latter water to again contact oxygen gas as aforesaid, and passing the reaction gas to a cooling zone to condense some of the hydrocarbons, leaving a mixture of acetylene and gaseous olefines.

References Cited by the Examiner UNITED STATES PATENTS 2,343,866 3/1944 Hincke 260679 2,789,149 4/1957 Bogart et al. 260679 2,908,733 10/1959 Sage 260-679 2,985,698 5/1961 Pechtold et a1. 260679 FOREIGN PATENTS 571,587 3/1959 Belgium.

ALPHONSO D. SULLIVAN, Primary Examiner.

I. ZIEGLER, D. S. ABRAMS, Assistant Examiners. 

1. A PROCESS FOR PRODUCTION OF ACETYLENE AND ETHYLENE, COMPRISING PYROLYZING A HYDROCARBON IN A STREAM OF HOT COMBUSTION GASES AND STEAM, THE STEAM BEING SUPPLIED TO THE COMBUSTIBLE GAS AND TO THE OXYGEN EMPLOYED TO FURNISH THE COMBUSTION GASES BY SATURATION WITH HOT WATER HEATED BY UTILIZING THE HEAT OF THE REACTION PRODUCTS, THE PROCESS BEING CARRIED OUT AT ABOUT TEN TO TWENTYU ATMOSPHERES ABSOLUTE PRESSURE, THE HYDROCARBON TO BE PYROLYZED BEING GASOLINE VAPOR, THE GASOLINE VAPOR BEING PREHEATED PRIOR TO INTRODUCTION INTO THE PYROLYSIS ZONE, STEAM BEING INTRODUCED INTO THE GASOLINE VAPOR BEFORE SAID PREHEATING. 